C# webapi Cors 服务器中的选项请求返回错误 404 未找到

Question

I am facing cors issue with Options preflight request shows 404 not found. Tested this in my local environment and my settings works completely fine. But when i tried to implement this in an actual IIS server, the Options preflight request shows 404 not found. My api is created as a web api project.

i had tried to set a preflight request handler as suggested in other post but its still not working. Is there any specific reason that it works only in local?

This section shows the option request:

General

Request URL: http://api.domain.cc/api/Login
Request Method: OPTIONS
Status Code: 404 Not Found
Remote Address: 192.168.10.5:80
Referrer Policy: strict-origin-when-cross-origin

Response Headers:
HTTP/1.1 404 Not Found
Content-Type: text/html
X-Powered-By: ASP.NET
Server: Domain
Date: Tue, 30 Mar 2021 07:54:34 GMT
Content-Length: 1245

Request Headers:

OPTIONS /api/Login HTTP/1.1
Host: api.domain.cc
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache
Accept: */*
Access-Control-Request-Method: POST
Access-Control-Request-Headers: authorization,content-type
Origin: http://site.domain.cc
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.90 Safari/537.36
Sec-Fetch-Mode: cors
Referer: http://site.domain.cc/
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9,zh-TW;q=0.8,zh;q=0.7,zh-CN;q=0.6

I had setup my web.config as below:

<system.webServer>
      <handlers>
          <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
          <remove name="OPTIONSVerbHandler" />
          <remove name="TRACEVerbHandler" />
          <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
      </handlers>
    <validation validateIntegratedModeConfiguration="false" />
    <modules>
      <remove name="ApplicationInsightsWebTracking" />
      <add name="ApplicationInsightsWebTracking" type="Microsoft.ApplicationInsights.Web.ApplicationInsightsHttpModule, Microsoft.AI.Web" preCondition="managedHandler" />
    </modules>    
  </system.webServer>

My web api config is as follows:

        public static void Register(HttpConfiguration config)
        {

            // Web API configuration and services
            EnableCorsAttribute cors = new EnableCorsAttribute(
                                        origins: "http://site.domain.cc",
                                        headers: "*",
                                        methods: "GET, POST, DELETE, PUT, OPTIONS")
            {
                SupportsCredentials = true
            };
            config.EnableCors(cors);

            // Web API routes
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );
        }

Answer 1

Can you test your api controller first by setting allowed origins in your web config to "*"

If this also returns 404 not found then something else is the problem and not the CORS.

Answer 2

I manage to fix the issue on my end. There are 2 things i did here.

1. Allow 'OPTIONS' verb in UrlScan as mentioned in this post 404 for web.api cors OPTIONS
2. Make sure the application pool is configured as ' Integrated ' mode.

The reason why my api is still returning error 404 for options request is because of my application pool was set to 'classic' mode previously.